Solid secondary battery and method of preparing the same

Abstract

A solid secondary battery and a method of preparing the same are provided. The solid secondary battery includes a cathode layer, an anode layer, and a solid electrolyte layer between the cathode layer and the anode layer, wherein the cathode layer includes a cathode current collector and a cathode active material layer on at least one side of the cathode current collector. The cathode active material layer includes a composite cathode active material, the composite cathode active material includes a composite of M 2 S, an alkali metal salt, and a two-dimensional carbonaceous structure, wherein M is an alkali metal, the alkali metal being Li or Na, the two-dimensional carbonaceous structure includes graphene, graphene oxide, reduced graphene oxide, or a combination thereof, and the composite includes a solid solution of the M 2 S and the alkali metal salt.

What is claimed is: 
     
         1 . A solid secondary battery comprising:
 a cathode layer;   an anode layer; and   a solid electrolyte layer between the cathode layer and the anode layer,   wherein the cathode layer comprises a cathode current collector and a cathode active material layer on at least one side of the cathode current collector,   wherein the cathode active material layer comprises a composite cathode active material,   wherein the composite cathode active material comprises a composite of M 2 S, an alkali metal salt, and a two-dimensional carbonaceous structure,   wherein M is an alkali metal, the alkali metal being Li or Na, and the two-dimensional carbonaceous structure comprises graphene, graphene oxide, reduced graphene oxide, or a combination thereof, and   wherein the composite comprises a solid solution of the M 2 S and the alkali metal salt.   
     
     
         2 . The solid secondary battery as claimed in  claim 1 ,
 wherein the two-dimensional carbonaceous structure is a two-dimensional carbonaceous structure doped with a dopant, and   wherein the dopant is an n-type dopant or a p-type dopant, and the dopant comprises nitrogen (N), phosphorus (P), boron (B), sulfur (S), fluorine (F), chlorine (Cl), bromine (Br), germanium (Ge), gallium (Ga), or a combination thereof.   
     
     
         3 . The solid secondary battery as claimed in  claim 1 ,
 wherein   an intensity derived from a first peak appearing at a diffraction angle of 2θ=18°±2.0° on an XRD spectrum of the composite cathode active material is smaller than an intensity derived from a second peak appearing at a diffraction angle of 2θ=18°±2.0° on an XRD spectrum of the two-dimensional carbonaceous structure utilized to prepare the composite,   wherein   the first peak has a first full width at half maximum (FWHM1) and the second peak has a second full width at half maximum (FWHM2), and   wherein   FWHM1 is greater than FWHM2, and   FWHM1 is 1° or more.   
     
     
         4 . The solid secondary battery as claimed in  claim 1 ,
 wherein an amount of the two-dimensional carbonaceous structure is about 0.1 parts by weight to about 20 parts by weight, with respect to 100 parts by weight of a total weight of the cathode active material layer, and   wherein the two-dimensional carbonaceous structure has a specific surface area of about 1 square meter per gram (m 2 /g) to about 50 m 2 /g, a diameter of about 1 micrometer (μm) to about 50 μm, and a thickness of about 100 nanometer (nm) to about 10 μm.   
     
     
         5 . The solid secondary battery as claimed in  claim 1 ,
 wherein the cathode active material layer further comprises a solid electrolyte, and   wherein the solid electrolyte comprises a sulfide-based solid electrolyte, an oxide-based solid electrolyte, a polymer solid electrolyte, or a combination thereof, and   wherein an amount of the solid electrolyte is about 10 parts by weight to about 60 parts by weight, with respect to 100 parts by weight of the cathode active material layer.   
     
     
         6 . The solid secondary battery as claimed in  claim 1 ,
 wherein the alkali metal salt is a lithium salt or a sodium salt, and the alkali metal salt is a binary compound or a ternary compound,   wherein the binary compound comprises LiI, LiBr, LiCl, LiF, LiH, Li 2 O, Li 2 Se, Li 2 Te, Li 3 N, Li 3 P, Li 3 As, Li 3 Sb, Li 3 Al 2 , LiB 3  or a combination thereof, or comprises NaI, NaBr, NaCl, NaF, Na 2 O, Na 2 Se, Na 3 N, Na 3 P, Na 3 As, Na 3 Sb, Na 3 Al 2 , NaB 3 , or a combination thereof, and   wherein the ternary compound comprises Li 3 OCl, LiPF 6 , LiBF 4 , LiSbF 6 , LiAsF 6 , LiClO 4 , LiAlO 2 , LiAlCl 4 , LiNO 3 , Li 2 CO 3 , LiBH 4 , Li 2 SO 4 , Li 3 BO 3 , Li 3 PO 4 , Li 4 NCl, Li 5 NCl 2 , Li 3 BN 2 , or a combination thereof, or comprises Na 3 OCl, NaBF 4 , NaPF 6 , NaAsF 6 , NaClO 4 , NaNO 3 , NaAlO 2 , NaAlCl 4 , NaNO 3 , Na 2 CO 3 , NaBH 4 , Na 2 SO 4 , Na 3 BO 3 , Na 3 PO 4 , Na 4 NCl, Na 5 NCl 2 , Na 3 BN 2 , or a combination thereof.   
     
     
         7 . The solid secondary battery as claimed in  claim 1 , wherein
 a molar ratio of the M 2 S to the alkali metal salt in the composite is about 50:50 to about 95:5, and   an amount of the two-dimensional carbonaceous structure is about 1 part by weight to about 30 parts by weight, with respect to 100 parts by weight of the composite.   
     
     
         8 . The solid secondary battery as claimed in  claim 1 ,
 wherein the composite has a particle size of 10 μm or less.   
     
     
         9 . The solid secondary battery as claimed in  claim 1 ,
 wherein the composite further comprises a carbonaceous material.   
     
     
         10 . The solid secondary battery as claimed in  claim 1 ,
 wherein the anode layer comprises an anode current collector and a first anode active material layer on the anode current collector.   
     
     
         11 . The solid secondary battery as claimed in  claim 10 ,
 wherein an anode active material of the first anode active material layer comprises at least one of a carbonaceous anode active material and a metal-based anode active material,   wherein   the carbonaceous anode active material comprises amorphous carbon, crystalline carbon, porous carbon, or a combination thereof, and   the metal-based anode active material comprises gold (Au), platinum (Pt), palladium (Pd), silicon (Si), silver (Ag), aluminum (Al), bismuth (Bi), tin (Sn), zinc (Zn), or a combination thereof.   
     
     
         12 . The solid secondary battery as claimed in  claim 10 ,
 wherein an anode active material of the first anode active material layer comprises a mixture of a metal-based anode active material and a carbonaceous material, a metal-based anode active material supported on a carbonaceous material, or a combination thereof.   
     
     
         13 . The solid secondary battery as claimed in  claim 10 ,
 wherein the anode layer comprises an anode current collector and a lithium host layer on one side of the anode current collector,   wherein the lithium host layer comprises a lithium host structure,   wherein the lithium host structure comprises at least one lithium host, the at least one lithium host comprising a carbonaceous lithium host, a metal-based lithium host, a polymer-based lithium host, or a combination thereof, and   wherein the solid secondary battery further comprises a first inactive member on the anode layer.   
     
     
         14 . The solid secondary battery as claimed in  claim 13 , further comprising a second anode active material layer between the anode current collector and the first anode active material layer,
 wherein   the second anode active material layer is a metal layer comprising lithium or a lithium alloy, and   the second anode active material layer is a plated layer, and   wherein a thickness of the first anode active material layer is greater than a thickness of the second anode active material layer.   
     
     
         15 . The solid secondary battery as claimed in  claim 1 , further comprising an inactive carbon member on at least one side of the cathode layer or the anode layer. 
     
     
         16 . The solid secondary battery as claimed in  claim 1 , wherein the solid secondary battery comprises
 about 10 parts by weight to about 80 parts by weight of the M 2 S,   about 10 parts by weight to about 40 parts by weight of the alkali metal salt, and   about 1 part by weight to about 20 parts by weight of the two-dimensional carbonaceous structure,   with respect to 100 parts by weight of the composite.   
     
     
         17 . The solid secondary battery as claimed in  claim 1 ,
 wherein the solid electrolyte layer comprises a solid electrolyte, a gel electrolyte, or a combination thereof,   wherein the solid electrolyte comprises a sulfide-based solid electrolyte, an oxide-based solid electrolyte, a polymer solid electrolyte, or a combination thereof, wherein the gel electrolyte comprises a polymer gel electrolyte,   wherein the sulfide-based solid electrolyte is at least one selected from among:   Li 2 S—P 2 S 5 ;   Li 2 S—P 2 S 5 —LiX, X being a halogen element;   Li 2 S—P 2 S 5 —Li 2 O;   Li 2 S—P 2 S 5 —Li 2 O—LiI;   Li 2 S—SiS 2 ;   Li 2 S—SiS 2 —LiI;   Li 2 S—SiS 2 —LiBr;   Li 2 S—SiS 2 —LiCl;   Li 2 S—SiS 2 —B 2 S 3 —LiI;   Li 2 S—SiS 2 —P 2 S 5 —LiI;   Li 2 S—B 2 S 3 ;   Li 2 S—P 2 S 5   13  Z m S n , m and n being each a positive number, and Z being one selected from among Ge, Zn, and Ga;   Li 2 S—GeS 2 ;   Li 2 S—SiS 2 —Li 3 PO 4 ;   Li 2 S—SiS 2 —Li p MO q , p and q being each a positive number, and M being one selected from among P, Si, Ge, B, Al, Ga, and In;   Li 7-x PS 6-x Cl x , 0<x<2; Li 7-x PS 6-x Br x , 0<x<2; and   Li 7-x PS 6-x I x , 0≤x≤2,   wherein the sulfide-based solid electrolyte comprises an argyrodite-type solid electrolyte,   wherein the argyrodite-type or kind solid electrolyte comprises at least one selected from among Li 6 PS 5 Cl, Li 6 PS 5 Br, and Li 6 PS 5 I, and   wherein the argyrodite-type or kind solid electrolyte has a density of about 1.5 gram per cubic centimeter (g/cc) to about 2.0 g/cc.   
     
     
         18 . The solid secondary battery as claimed in  claim 1 ,
 wherein the anode layer comprises an anode current collector,   wherein at least one of the cathode current collector or the anode current collector comprises a base film and a metal layer on at least one side of the base film, and   wherein the base film comprises a polymer, the polymer comprising polyethylene terephthalate (PET), polyethylene (PE), polypropylene (PP), polybutylene terephthalate (PBT), polyimide (PI), or a combination thereof, and   wherein the metal layer comprises indium (In), copper (Cu), magnesium (Mg), stainless steel, titanium (Ti), iron (Fe), cobalt (Co), nickel (Ni), zinc (Zn), aluminum (Al), germanium (Ge), lithium (Li), or an alloy thereof.   
     
     
         19 . A method of preparing a solid secondary battery, the method comprising:
 milling a composition comprising M 2 S, an alkali metal salt, and a two-dimensional carbonaceous structure;   adding thereto a two-dimensional carbon nanostructure to obtain a composite, and milling the composite;   preparing a cathode by utilizing a composition containing the composite that is mixed with a binder;   preparing an anode; and   applying an electrolyte between the cathode and the anode, to thereby produce the solid secondary battery as claimed in  claim 1 .   
     
     
         20 . The method as claimed in  claim 19 ,
 wherein a carbonaceous material is added to the composition in the milling the composition.